This invention relates to ac motor controllers, and in particular, to an ac motor controller which receives an ac source-voltage having a frequency within a wide range, and automatically provides a load-voltage to an ac motor at a substantially fixed frequency, regardless of the frequency of the ac source-voltage.
Large, mobile or transportable units for housing personnel or electronic equipment are often equipped with heavy duty air-conditioning systems. Such systems are usually powered by an ac source-voltage provided by the power utility in the location where the mobile units are deployed. The ac motors that drive the various components, such as fans and compressors, of the air conditioning units are designed to operate a particular frequency of ac voltage. However, the frequency of the local power utility's line voltage is not always compatible with the requirements of the ac motors of the mobile unit air conditioning systems. The problem is particularly acute when such mobile units are deployed overseas where the power frequency can change from country to country.
Manually operated motor controllers or frequency converters have been used to permit the air conditioning systems on such mobile units to be used with a range of power frequencies. However, such manual controllers leave much to be desired because they rely on the operator to properly set the controller to provide the proper frequency conversion and because the frequency range for which they are useful is relatively limited.